The present invention is directed to preparing traceable copies of digital content and, in particular, to adding a unique identifier to the digitally encoded content in a manner which does not alter the intended effect of the content when the content is played back but which can be readily decoded to determine the source of a copy of the digital content.
The present invention relates to a problem that confronts digital audio and video-content providers when such content and/or other copyrightable material is digitally encoded and distributed, for example over a network or via writable storage media: copies of this material are indistinguishable from the original digital content. At the same time, home computers have become common, if not ubiquitous, and distribution methods such as network connections (e.g. the Internet) and peripheral drives that can transfer information to writable media are increasingly affordable. Naturally, these distribution methods can also receive the digital content from others who are connected to the network or from read-only media, so even a nominally honest user can be tempted to make unauthorized copies. This scenario is now affecting the digital audio market because CD-R (write-once) discs have become very inexpensive.
Presently, video DVD content is disguised by the Contents Scramble System (CSS). (For an overview of CSS, see Michael Moradzadeh xe2x80x9cLicensing Requirements for the CSS DVD Copy Protection Method,xe2x80x9d Intel Corporation, 1997.) Unscrambled digital video outputs are not provided on consumer-market players, and current DVD-ROM drives that play video DVD discs output scrambled content to a separate hardware decoder. A hardware decoder represents extra cost, but software implementations are also possible and have even been licensed. Cheap unlicensed CSS decoder software, has already appeared on a website as freeware. Such software could give any personal-computer user, even one who lacks specialized knowledge, full access to the content on video DVD discs. At the present time, writable DVD discs are not widely available at the full capacity (4.7 Gbytes) of video DVD discs, but DVD technologists are working on that, too.
Thus it appears that the rapid pace of technology may stunt the growth of the video DVD market within a few years of creating it. It is not surprising that a DVD application that used strong encryption (called DIVX) appeared (see xe2x80x9cDigital Versatile Delirium: DIVX vs. DVD-Video,xe2x80x9d InterActivity Magazine, Oct. 1998.) The DIVX system was meant to free consumers from the danger of incurring late charges on rented discs. In fact, DIVX discs were not returnable. Initially they could be played for only 48 hours. After that 48-hour period elapsed, the disc could be made to be played again, but with additional charges. Billing and access to encryption keys were managed from a central location through telephone lines connected to each player. However most existing DVD players do not have the strong-decryption circuitry and telephone interfaces necessary to receive authorization and play DIVX discs. Some consumers postponed purchasing either type of player for a while, thinking regular DVD players might become obsolete. Meanwhile DIVX players are a market failure. Although it is likely that the cost of the extra circuitry in the DIVX players would have decreased over time, consumers apparently did not want to keep discs that can cause unexpected charges to appear on their credit-card statements, or require phone authorization at all.
The security of DIVX is also questionable. It is difficult to devise a copy-protection scheme for identical mass-market discs relying exclusively on information contained on the discs themselves. This is because personal computers are more powerful than players. Attempts to put functions into a player that cannot be duplicated in software in a personal computer have been overtaken by advancing technology. Also, DIVX discs become unusable in DIVX players when the players can no longer make telephone connections to DIVX service centers.
Clearly, the problem of copy protection remains unsolved, and there is still time to consider new approaches. One aspect of the problem that appears to have been overlooked is that, when consumers can afford to use writable media for copying, the opportunity arises for content providers to use the same writable media for distribution. At that time, a content provider will also have an opportunity to customize the content for the intended customer. This customization might add value for the paying customer while subtracting value for other persons who have different needs and preferences. Indeed, mass customization may well turn out to be a new paradigm for many industries in the 21st century (see Rosemary Coates, xe2x80x9cMass Customizationxe2x80x94Manufacturing Postponement for the Next Century,xe2x80x9d Computer Sciences Corporation White Paper, 1997).
A prior-art method of customizing content introduces information identifying the recipient as described in U.S. Pat. No. 4,595,950 entitled METHOD AND APPARATUS FOR MARKING THE INFORMATION CONTENT OF AN INFORMATION CARRYING SIGNAL. Here, the content on the distribution media is not usefully customized, but it is encoded. The assumption is made that the recipient cannot access the content other than through a decoder that adds information identifying the recipient. Subsequent copies of the playable content are thus traceable, and thereby protection against such copying is obtained. One disadvantage inherent in this method is that the installed base of encoders provides an upper limit to the market for content and vice versa.
There is voluminous prior art for embedding a message in a digital work. For example, U.S. Pat. No. 5,809,160 xe2x80x9cMETHOD FOR ENCODING AUXILIARY DATA WITHIN A SOURCE SIGNAL,xe2x80x9d is directed to the problem of identifying candidate points in an image at which data can be unobtrusively embedded through subtle modifications of pixel values. This method is conditioned on identifying the presence of signature points in an image. It is therefore necessary to analyze a subject image in order to retrieve data that may be hidden therein. However, digital works are typically stored or transported in large numbers of data objects that are substantially smaller than is required to represent a complete image. It is more convenient to detect hidden data directly from these small data objects rather than to assemble many of them into an image and then extract the data by image processing techniques. Moreover, some digital works may not represent images or analog signals of any kind.
The present invention is embodied in a method and apparatus for preparing a digital work in sequential default data objects for subsequent customization of two or more distinct copies. By this method, digitally distinct alternate versions of each data object of the digital work are prepared such that each alternate version of each data object is judged to produce an acceptable variation in said digital work. The various objects are then saved in a content database.
According to another aspect of the invention, a method of encoding the digital work to identify a particular copy further begins by preparing enforcement data for each customized copy sufficient to trace the copy to a customer to whom the copy is going to be distributed. The enforcement data with customer identification information is then recorded. The customized copy is assembled by selecting successive data objects in the work as either the data object or one of the alternate data objects from said content database depending on successive values of the enforcement data.
According to another aspect of the invention, the identification data for a particular copy may be reconstructed by discriminating between said default data object and said alternate data object, using the content database, as the successive data objects of said copy are processed. The enforcement data object is reconstructed by assigning values in successive positions responsive to the discrimination. Once the enforcement data object is obtained, the associated identification information for the customer is recovered from the database.
According to yet another aspect of the invention, the identification of the enforcement data object may be made from less than the full object. This aspect of the invention starts by selecting a one-way hash function that is used to compute digital fingerprints of the default and alternate application data in each data object, the fingerprints containing at least one bit but fewer bits than the application data. This aspect of the invention continues by storing the fingerprint data in the copyright management area of each data object, wherein, for each data object, the fingerprint data differs in at least one bit position from the fingerprint data of the alternate application data object. In this embodiment, the fingerprint data of the copy is compared to fields of the database.
According to another aspect of the invention, a method for authenticating copies of a digital work is provided. The method begins by accessing authentication information to obtain an authentication object. The encrypted fingerprint data is then concatenated to the authentication object. At the receiving end, the authentication data is decrypted using decryption data available to the recipient. The decrypted authentication data is then parsed into decrypted fingerprint data which are matched to the fingerprint data of the digital copy. The copy is determined to be authentic when the fingerprint data in the database matches the decrypted fingerprint data.